The invention relates generally to ultrasonic inspection systems and methods and more specifically to ultrasonic inspection systems and methods for micro-structural evaluation of objects.
Many mechanical failure modes include a long duration first step in which microstructural damage and/or change accumulates in a region, followed thereafter by occurrence of observable cracks and failure. Of the overall service lifetime of a part, only a small amount of life remains once cracks are observable.
Cracks that are above certain threshold sizes, and within certain specified regions, may be detected by existing ultrasound or eddy current techniques. For example, in conventional ultrasonic inspection, ultrasound signals or pulses are transmitted and echo signals are received by a transducer. Discontinuities, such as cracks, can be detected when their echoes are greater than that of the background noise.
Typically, the microstructure of a material in the part determines the various applications in which the parts can be used. Grain size is one important characteristic that is measured to ensure its value lies between a required range, to satisfy the fatigue and creep requirements of the part. It would therefore be desirable to detect regions, which deviate from the specified grain size, as such regions are likely to have undesirable material characteristics. However, when such regions are embedded within the part, detecting the microstructures is a challenge. Also, different product shapes and different processing procedures can produce a variety of grain shapes, which may constrain the ability to measure the grain size.
Accordingly, there is a need to non-destructively detect microstructures of varying sizes, which in turn assists in predicting where a crack might occur in the part.